The art has long recognized that acoustical means may be used for determining a portion of the trajectory of a projectile, and the art, generally, has used such acoustical means for locating the point at which a projectile passes into or near a training target for scoring the accuracy of small arms fire, in lieu of the more conventional paper targets. An example of the foregoing is U.S. Pat. No. 4,514,621. Basically, these devices operate by means of a grid of acoustical sensors in which the plane of the sensors is normal to the trajectory of the projectile, e.g. a rifle bullet. As the bullet passes through that grid of sensors, the sensors can locate the passage of the bullet through that grid of sensors by calculating the time delays of the sensors.
When two such grids are spaced apart, one behind the other, and the path of a bullet passes through both of the grids, a portion of the trajectory of a bullet may also be determined, and U.S. Pat. No. 3,445,808 is representative thereof. That patent also points out that if a such a dual grid system is deployed on a military vehicle, e.g. a helicopter, and enemy fire passes through the two spaced-apart grids, the general direction of the trajectory of that fire may be determined.
Similar methods for locating the passage of a bullet may use other types of sensors, such as electrical resistance elements, rather than acoustical transducers, and U.S. Pat. Nos. 3,585,497 and 3,656,056 are representative thereof.
Rather than using a grid of acoustical sensors, curved elongated hoops with acoustical transducers at ends thereof may be used. When a bullet passes within the vicinity of the curved hoops, the position of the bullet passing such curved hoops can be calculated, and U.S. Pat. No. 4,351,026 is representative thereof.
Curved hoops may also be used where the target is moving within a defined field normal to the hoops, and U.S. Pat. No. 5,025,424 is representative of that technology.
Somewhat similarly, U.S. Pat. No. 4,885,725 suggests a plurality of triangularly arrayed, mechanically connected acoustical transducers, instead of curved hoops, for determining the point in which a bullet passes the target area and for providing some indication of the velocity of that bullet.
The foregoing patents are, primarily, directed toward training devices for scoring the accuracy of a trainee's fire, although, as mentioned above, U.S. Pat. No. 3,445,808 suggests the use of double acoustical grids for determining the general direction of enemy fire toward a military device, such as a helicopter.
Further, U.S. Pat. No. 4,659,034 suggests the use of a plurality of transducers disposed on a movable (towed) target and, by use of the transducers, determining the accuracy of fire toward that target. That accuracy of fire includes how close the projectile comes to the towed target (referred to as the miss-distance). U.S. Pat. No. 4,323,993 similarly determines a miss-distance by acoustical transducers, and, particularly, in this patent the miss-distance is calculatable even though the projectile misses the towed target altogether.
U.S. Pat. No. 4,805,159 provides a method for estimating the miss-distance between a projectile and a movable training target. In making such estimation, at least a portion of the trajectory of the projectile is also estimated. However, as that patent points out, the estimations of at least a portion of the trajectory of the projectile involves a number of possible estimates of the actual projectile path, and to eliminate erroneous estimates, additional transducers are used for consecutively selecting true estimates from erroneous estimates.
Thus, in general, the prior art, mainly, uses sensors, especially acoustical transducers, in various spatial arrangements for determining the miss-distance of a projectile passing through or near a target. Some of these systems in the art may provide a general direction of a local trajectory of the projectile, but these systems are not capable of providing accurate information as to the entire path of the projectile, and, hence, the position of the source of that projectile. In addition, these prior art systems, whatever their configuration, must have pre-knowledge of the direction and/or the velocity of the projectile, in order to determine the local trajectory of the projectile.
Thus, the prior art systems are useful essentially only in training exercises where either or both of the direction or velocity of the projectile is known, and such systems have essentially only been employed in such exercises. Thus, the systems are not applicable to battlefield conditions where it is important to know essentially the entire direction of the trajectory of a projectile, the miss-distance of that projectile, the approximate caliber or mass of that projectile, and the approximate origin of the source of that projectile, and under conditions where the velocity and/or direction of the projectile is unknown. All of this information is most useful in battlefield conditions where a military unit, under attack, cannot visually or by other human senses determine the direction, miss-distance, caliber and source of enemy fire.
This is often the case in modern warfare. For example, in modern tank warfare, the battlefield may span many kilometers, and incoming enemy fire, for example, shell fire, is confused with other background battle noises and noises produced by friendly fire. For example, a tank commander may hear the distinctive sounds of a near-miss enemy shell, but in the confusion of battle noises, the tank commander may not be able to determine either an approximate azimuth or elevation of the trajectory of that enemy shell. Thus, the tank commander cannot determine whether the shell is being fired from a long distance, or a very short distance, or whether the fire is coming from the front, rear or sides, or even the approximate caliber of that shell fire. Without such information, for example, the tank commander cannot quickly and positively respond to such enemy fire, and the dangers of a near-miss previous shell can increase markedly with succeeding enemy shells, which makes return suppressing fire of utmost importance.
Also, the prior art devices are not capable of scoring training fire where the training fire is of unknown velocity and/or direction. This is usually the situation in maneuver training fire where, for example, moving and roving tanks are firing on a target, e.g. an obsolete tank.
As can, therefore, be appreciated, it would be of substantial advantage in the art to provide apparatus and methods for determining essentially the entire trajectory of a supersonic projectile of unknown velocity and direction, such as shell fire, or even small arms fire. That trajectory will provide the approximate position of the origin of that incoming enemy fire. In addition, when the miss-distance of such incoming enemy fire is calculated, the likelihood of additional and eminent more accurate enemy fire is determinable. This provides an opportunity for immediate and effective return suppressing fire. Further, it would be of advantage to provide such apparatus and methods which are also adaptable to maneuver training fire.